Road Identification System Using Enhanced Cross-Section Targets

ABSTRACT

An aspect of the present disclosure is directed to and provides radar-reflecting systems and apparatus that employ metasurfaces to produce enhanced radar cross sections that are greater than those produced by the geometry of the surfaces alone. Another aspect of the present disclosure is directed to and provides heat-ducting systems and apparatus that include metasurfaces. A further aspect of the present disclosure is directed to and provides cards with metasurfaces. Exemplary embodiments utilize fractal plasmonic surfaces for a metasurface.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of and priority to thefollowing applications: U.S. Provisional Patent Application No.62/583,740, filed November 9, 2017, and entitled “Fractal Based RadarTargetting and Identification for Autonomus Vehicle Highwars”; U.S.Provisional Patent Application No. 62/593,636, filed Dec. 1, 2017, andentitled “Metasurface-Based Radar Targeting and Identification forAutonomous Vehicle Highways”; and, U.S. Provisional Patent ApplicationNo. 62/618,165, filed Jan. 17, 2018, and entitled “Fractal MetamaterialApplications”; each of which applications is hereby incorporated hereinby reference in its entirety.

BACKGROUND

Automotive radar systems have been developed for to provide variousbenefits to drivers and pedestrians. For example, such radar systems maybe used for adaptive cruise control, collision warning, automaticdistance control, pre-crash detection, aiding in parking, cut-incollision warning, blind spot detection, and rear-end collision warning.

While such radar systems have been shown to be robust in use, theperformance of the systems is typically limited, in use on vehicles andother locations, by the requirement of relatively large structures inorder to produce large enough radar cross sections for the radar systemto be able to detect those structures. The structures can act as“markers” and/or fiducial points by which the radar system “sees” andnavigates the vehicle; during navigation, the radar system and vehicleare typically bounded or guided by the placement of the structures onthe road, or other vehicles, or in raised structures on or adjacent tothe road.

SUMMARY

An aspect of the present disclosure is directed to and providesradar-reflecting systems and apparatus that employ metasurfaces toproduce radar cross sections greater than those produced by the geometryof the surfaces alone.

Another aspect of the present disclosure is directed to and providesheat-ducting systems and apparatus that include metasurfaces.

A further aspect of the present disclosure is directed to and providescards with metasurfaces.

Exemplary embodiments utilize fractal plasmonic surfaces for ametasurface.

These, as well as other components, steps, features, objects, benefits,and advantages, will now become clear from a review of the followingdetailed description of illustrative embodiments, the accompanyingdrawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings are of illustrative embodiments. They do not illustrate allembodiments. Other embodiments may be used in addition or instead.Details that may be apparent or unnecessary may be omitted to save spaceor for more effective illustration. Some embodiments may be practicedwith additional components or steps and/or without all of the componentsor steps that are illustrated. When the same numeral appears indifferent drawings, it refers to the same or like components or steps.

FIG. 1 shows a radar-reflective road identification (“RDID”) system, inaccordance with exemplary embodiments of the present disclosure.

FIG. 2 shows features of a RDID patch, in accordance with exemplaryembodiments of the present disclosure.

FIG. 3 depicts a set of examples of fractal plasmonic surfaces (FPS)that can be used or integrated with radar reflectors, in accordance withthe present disclosure.

FIG. 4 shows a fractal plasmonic surface configured as a heat-ductingsystem, in accordance with further embodiments of the presentdisclosure.

FIG. 5 shows a card including a fractal plasmonic surface, in accordancewith other embodiments of the present disclosure.

DETAILED DESCRIPTION

An aspect of the present disclosure is directed to and provides devicesand structures that incorporate plasmonic surfaces or structuresembedded or included within the devices and structures and/or disposedon a surface or surfaces of the devices and structures. The plasmonicsurfaces or structures can include metamaterials, and can be referred toas “metasurfaces” or “metastructures.” The metamaterials can includestructures smaller than a wavelength of radiation of interest, e.g.,used in a radar band. In exemplary embodiments, the plasmonic surfacesinclude fractal features, and can accordingly be referred to as “fractalplasmonic surfaces” or “FPS.” Fractal plasmonic surfaces (FPS) arecomposed of, or include, fractal shapes which are closely spaced(close-spaced) and disposed upon or included a surface or structure.Without limiting the scope of the present disclosure, evanescent surfacewave production through evanescent-wave transfer is believed to be thedominant mechanism by which information, power, and/or radiation areconveyed as radiative transfer on or in these surfaces and/orstructures.

An exemplary aspect of the present disclosure is directed to andprovides for the inclusion of plasmonic surfaces or structures with,inside, or on structures that are used for automobile use, includingmanned and unmanned (i.e., autonomous) vehicles. Road and automobilestructures that such plasmonic surfaces or structures may be used withinclude, but are not limited to, road reflectors, stop signs, roadbarriers, toll booths and plazas, tracks or guides used with (e.g.,embedded in) road surfaces, and components of road-going automobiles(including motorcycles) such as bumpers, frames, etc., as well as otherstructures that would normally be encountered in travel. Such plasmonicsurfaces and/or structures can be used for systems for enhancing theperformance of location-determination, safety, and/orcollision-avoidance for vehicles, for non-limiting examples.

Exemplary embodiments of the present disclosure have application tomanned and/or autonomous vehicles on highways, by employingmetasurface-based reflectors for reflecting radar signals/radiation,e.g., from a vehicle's on-board radar. FIG. 1 depicts a system 100employing radar-reflective materials, in accordance with an illustrativeembodiment. System 100 includes conductive or otherwise highlyradar-reflective material configured as “patches” 110 and 120. Thesepatches 110 and 120 incorporate a metamaterial surface (metasurface)having or producing a radar cross section which is higher than one of aconductive continuous sheet of the same size. The patches 110 and 120can be used in conjunction with a radar system 130, e.g., an operationaltransceiver, onboard an automobile 140. In exemplary embodiments, themetasurface may be or include a FPS. Thus, embodiments of the presentdisclosure can provide means for scattering the incident radarwaves/energy/radiation through use a type of structure, e.g., ametasurface or metastructure, having a radar cross section far largerthan that due solely to its physical size in the absence of themetasurface.

The metasurface used for the patches 110, 120 can act as anidentification system, or a super-scatterer, having a larger radarcross-section than the radar cross-section of the unit without themetasurface. In exemplary embodiments, plastic road reflectors, whichare built as plastic pieces that reflect light, can also incorporate oneor more metasurface or FPS features in accordance with the presentdisclosure. Exemplary embodiments of a plasmonic-surface based roadfeature are described in further detail below.

FIG. 2 depicts an example of conductive metasurface 200 for use in aradar road reflector, according to exemplary embodiments of the presentdisclosure. FIG. 2 shows rectangles of conductor surrounded by smallerrectangles, e.g., 210 and 220, which are connected by a thin lattice 240and repeated across the area. The dark regions, e.g., 230, are adielectric substrate. Any suitable material(s) can be used for theconductors, e.g., conductive paint, copper traces, etc. Any suitablematerial(s) can be used for the substrate, e.g., FR4, polyimide, etc.While FIG. 2 depicts an exemplary embodiment of a metasurface 200,metasurfaces in accordance with the present disclosure can include othershapes or unit cells. Examples include, but are not limited to,split-ring resonators, nested triangles, transmission line equivalents,posts, honeycomb structures with wells, etc. In exemplary embodiments,metamaterial(s) used can produce a negative index of refraction forradiation at the operational wavelength(s), e.g., SRR or LRR band.

In exemplary embodiments, resonators or cells included on themetasurface (e.g., patches 110 and 120 of FIG. 1) are separated fromothers. Resonators or cells, e.g., conductive shapes, may be isolatedfrom the other(s) meaning that no conductive material is present whichconnects them, e.g., they are in galvanic isolation from one another.Examples of such physically-isolated cells or resonators are shown inFIG. 3.

FIG. 3 depicts a set 300 of examples of fractal plasmonic surfaces (FPS)that can be used or integrated with radar road reflectors, in accordancewith the present disclosure. Two different FPS configurations are shown:a four-lobed design 310, and a saw-tooth design including a Sierpinskitriangular mesh 320. Design 310 includes an array 312 of individualfour-lobed resonators or cells, e.g., 312-1, that are disposed on asubstrate 310. The cells (which may also be referred to as “unit cells”or “resonators) are physically separate from one another. They are notin direct connection by any conductive material or path. Thisarrangement can be considered as galvanic isolation.

As shown the cells have a characteristic dimension “A,” e.g., a heightor major-axis, which can be designed or selected based on a particularoperational wavelength or range of wavelengths used for a radar systemused with the FPS. Further as shown, the individual cells or resonatorscan be separated from adjacent cells or resonators by a separationdistance B, which can also be designed or selected based on anoperational wavelength or wavelengths.

With continued reference to FIG. 3, design 320 employs a trianglegenerator motif, e.g., 322, as cutouts or voids within conductivematerial (lighter shading) on a substrate 324. As shown, design 320 canhave a characteristic dimension C, e.g., a width or height.

Thus, as described for FIGS. 1-3, radar-reflecting structures accordingto the present disclosure can be shaped or configured as metamaterialsurfaces having arrangements or arrays of closely packed resonators (orcells) that function as radar scatterers. These radar scatters can bemade into desired or appropriates sizes, which produce a radar crosssection far higher than due to their physical size alone. Thus suchmetasurfaces or structure(s) containing such a metasurface ormetasurfaces can constitute ideal road markers or “identificationmarkers,” also referred to herein as “patches,” “radar road reflectors,”or “RDID patches,” where RDID refers to “road ID”. Such RDID patches maybe used advantageously, for example, in collision avoidance systems,marking, and location identification on highways and on vehicles. TheseRDID patches may be small enough to easily place on or into a roadsurface, another vehicle's body or bumper, obstacles on or near theroad, traffic cones or jersey style barriers or fences, trees, and soon. In exemplary embodiments, cells of these RDID patches may be fractalin shape and may be referred to as fractal RDID patches. RDID patchesmay be embedded within or covered by protective materials such as hardplastics or composites that do not impede or prevent the operation ofthe RDID patch (metasurface) with incident radiation. For example, aRDID patch may be encased in a hard plastic or resin, such as a highimpact traffic-bearing plastic, that is sufficiently strong and durablefor use on or in a road lane reflector or guidance reflector that isexpected to be subject to the weight, pressure, and impact of vehiclespassing over it. A RDID patch may be encased, embedded, or otherwiseembodied in a traffic-bearing reflector that includes a visible-lightreflector. Embodiments of a RDID patch can include more than onemetasurface, e.g., FPS, for operation at multiple wavelengths ofincident radiation. Such multiple metasurfaces may be stacked in layers,e.g., each having their own substrate, or may be disposed or formed onthe same substrate.

In an additional aspect of the invention, a RDID patch or patches mayemploy a metasurface having combinations of shapes that make up themetasurface, with at least some difference in shape between theconductive elements of the patch or patches. This arrangement canproduce a frequency-dependent radar cross section by which abroad-banded radar is able to see different maximum cross sections atdifferent frequencies. The arrangement of frequencies of such may beused effectively as an encoding mechanism, e.g., by which the RDID patchencodes information, such as location, presence of one or more obstacles(e.g., “obstacles ahead” or “falling rock”), and the like. Thereflections can be more intense at some frequencies than others, basedon the shapes. The arrangement, in frequencies, of these “reflectionbands” can act as an encoding.

Embodiments of the present disclosure can be designed for andimplemented for operation with or over a general frequency range, suchas well-known microwave RF bands, but the scope of the presentdisclosure is not limited to those defined frequency ranges; and, inother embodiments other different or overlapping electromagneticfrequency bands (including those in the optical ranges of UV, visible,and IR) can be realized.

A further aspect of the present disclosure is directed to and providesmethods of producing, acquiring, processing, and/or displaying theinformation procured by use of a fractal RDID patch or patches,incorporating (vehicle) on-board computers, transmitters, receivers,antennas, displays, as well as vehicles so equipped; accordingly,embodiments of the present disclosure can facilitate autonomous vehicle(guidance) systems.

In exemplary embodiments, systems according to the present disclosureuse conductive or otherwise highly radar reflective “patches” havingmetasurfaces incorporating at least one shape which is at least, inpart, described as a substantially self-similar shape, or fractal,having at least two iterations of application of a motif (generatormotif). Such radar reflecting structures—with resonators that are shapedas fractals—may be referred to as “fractal RDID patches.” Fractal RDIDpatches can be small enough to easily place on or into a road surface, avehicle's body or bumper, obstacles on or near a road, traffic cones orjersey style barriers or fences, trees, and the like. These fractal RDIDpatches may also be made into a close spaced array such as a fractalmetamaterial.

Exemplary embodiments of FPS and/or metasurface-based RDID structuresare designed for use at certain frequencies used in automotive radarapplications. For example, a RDID structure (e.g., lane marker)according to the present disclosure may be configured for operation at24 GHz, e.g., as coinciding with so-called short-range radar (“SRR”). At24 GHz, the operational wavelength is approximately 12.5 mm (or, 0.5inches), which can be used then to design the size and separationdistance used for the FPS or metasurface features. As another example, aRDID structure (e.g., lane marker) according to the present disclosuremay be configured for operation at 77 GHz or within the range of 76-81GHz, e.g., as coinciding with SRR, so-called medium-range radar (“MRR”),and/or so-called long-range radar (“LRR”). At 77 GHz, the operationalwavelength is approximately 4 mm (or 0.157 inches), which can be usedthen to design the size and separation distance used for the FPS ormetasurface features.

A characteristic dimension of each resonator or cell used for a FPS ormetasurface-based (metasurface) structure can be derived from or basedon an operational wavelength of incident radiation, e.g., such as thatfrom an automotive radar system (e.g., within the range of wavelengthsfrom about 3 mm to about 13 mm). For example, assuming an operationalwavelength of 4 mm (similar to that of a SRR system), a characteristicdimension of a cell within the FPS or metasurface or structure could be0.5 mm (i.e., ⅛ of a wavelength, or lambda). Using an operationalwavelength of 12.5 mm, a characteristic dimension of a cell within theFPS or metasurface or structure could be 3.125 mm (i.e., ⅛ of awavelength, or lambda). Of course, other values can be used for acharacteristic dimension (e.g., major or minor axis, diameter, height,etc.) of a cell or resonator vis-à-vis an operational wavelength. Forexample, a cell or resonator may have a characteristic dimension (e.g.,major or minor axis, diameter, height, etc.) on the order of theoperational wavelength (or for a range of wavelengths, a wavelengthwithin or at a bound of the range). For further example, a cell orresonator may characteristic dimension of about ½, ⅓, ¼, ⅕, ⅙, 1/7, 1/9,1/10, etc. of the operational wavelength (or for a range of wavelengths,a wavelength within or at a bound of the range). For further example,other values may be used for a characteristic dimension of a cell orresonator of a FPS or metasurface. Metasurfaces can accordingly bedesigned for operation with particular wavelengths or frequency bands ofincident radiation, e.g., LRR, MRR, and/or SRR automotive radar bands.

Cells or resonators of a FPS or metasurface-based structure (e.g., aRDID) are preferably separated by a separation distance that is afraction of an operational wavelength or nominal wavelength of anautomotive radar system. Examples of such a separation distance caninclude, but are not limited to, ¾, ⅔, ½, ⅓, ¼, ⅕, ⅙, 1/7, ⅛, 1/9, 1/10,1/11, 1/12, 1/20, etc. of the operational wavelength (or for a range ofwavelengths, a wavelength within or at a bound of the range). Forfurther example, other values may be used for the separation distance orseparation distances of a FPS or metasurface; a distribution ofresonators or cells within a FPS or metasurface need not be uniform andcan have a non-uniform spatial distribution. Metasurfaces canaccordingly be designed for operation with particular wavelengths orfrequency bands of incident radiation, e.g., LRR, MRR, and/or SRRautomotive radar bands.

Further embodiments of the present disclosure are directed to and canprovide metasurfaces that are useful outside of radar reflection. Forexample, metasurface-based heat-direction systems can utilize a layer orlayers of FPS or metasurface on a substrate to direct infrared energy indesired directions. FIG. 4 shows an example of such a system 400utilized for a window. System 400 includes a metamaterial surface(metasurface) 402 including a plurality of resonators (or, cells) 410disposed on a substrate 430. The cells of the metasurface may beconfigured in exemplary embodiments to transfer radiation at infrared(“IR”) wavelengths, e.g., any of near-IR, medium-IR, and far-IRwavelengths). The metamaterial surface 402 may be disposed on a windowpane 440 of a window, as shown. In exemplary embodiments, the substratemay be made of a transparent or translucent material.

While metasurface 402 is shown as having resonators, e.g., 410-1, of agiven size, the indicated size is primarily for the purpose ofillustration. In exemplary embodiments, the resonators of anIR-direction systems (which may also be referred to as “IR-ducting” or“heat-ducting” systems) such as system 400 are designed and fabricatedto have characteristic dimensions and/or separation distances selectedfor use at infrared wavelengths, as described previously.

The metasurface, or metastructure (e.g., FPS) 402 within or on thewindow pane 440 can transfer the infrared energy off to the side(s) ofthe window edge thereby preventing most of the infrared energy frompassing through the window into the, e.g., interior environment of arelated structure or building. In addition, the infrared radiation,being transferred to the side or edges of the window, may be collectedand used, e.g., for energy harvesting and/or heating. While system 400is shown with metamaterial surface 402 on one side of the window pane440, the metasurface 402 could, instead or in addition to, be disposedon the opposite surface of the window pane, e.g., for facilitating theprevention of infrared energy from leaving an interior space of abuilding or structure having the window pane 440. Accordingly,embodiments of the present disclosure can be used for heating and/orcooling of structures or areas. Exemplary embodiments of such a systemcan be designed for use with incident radiation of wavelengths between,e.g., 700 nm to 1 mm; other wavelengths may be used or designed for inalternate embodiments.

Further embodiments of the present disclosure include metasurfaces thatcan be used for identification and/or as keys or cards. FIG. 5 shows oneexample of a card or card system 500 with plasmonic metasurface 502, inaccordance with the present disclosure. The metasurface 502 includes aplurality of resonators 510 disposed on a substrate 520. The substrate520 can be applied to a card, e.g., a pre-existing credit card or roomkey card 530. The card 500 may be made of plastic or other suitablematerial. As shown, in exemplary embodiments the plurality of resonatorscan be configured as a FPS having separated resonators. Such a device500 can act as an identification system through wireless transmission,and may for example be a vetting mechanism for positive identification Acard having a metasurface may also be used for example to access doorlocks hotel rooms and so on. Such a card may be used for or withnear-field communication systems. Accordingly, a card having ametasurface, metastructure, and/or FPS, may be used to activateswitches, provide identifying information, and so on. In exemplaryembodiments, the substrate may be made of a transparent or translucentmaterial. Exemplary embodiments of a metasurface card (e.g., similar tothat of system 500) can be designed for operation at 13.56 MHz, e.g.,according to the ISO/IEC 18000-3 standard (including MODE 2). Exemplaryembodiments may be used for RFID.

Exemplary Embodiments

Clause 1: A radar road reflector comprising:

a metasurface having a plurality of resonators, wherein the metasurfaceincludes a substrate supporting the plurality of resonators, wherein themetasurface has an area, wherein the plurality of resonators supportplasmonic transfer of incident radiation across the surface, and whereinthe metasurface provides a radar cross section that is larger than aradar cross section of the area of substrate itself without theplurality of resonators.

Clause 2: The radar road reflector of clause 1, further comprising asupport that supports the metasurface.

Clause 3: The radar road reflector of clause 2, wherein the support isconfigured for application to a road surface.

Clause 4: The radar road reflector of clause 3, wherein the support ismade of high-impact plastic.

Clause 5: The radar road reflector of clause 1, wherein the metasurfacecomprises a fractal plasmonic surface (FPS).

Clause 6: The radar road reflector of clause 5, wherein the FPScomprises a plurality of resonators having fractal shapes separated fromone another.

Clause 7: The radar road reflector of clause 6, wherein resonators ofthe FPS are separated by a separation distance of about 1/10 to about ½of a radar wavelength of operation.

Clause 8: The radar road reflector of clause 7, wherein the radarwavelength of operation corresponds to a SRR band at 24 GHz.

Clause 9: The radar road reflector of clause 7, wherein the radarwavelength of operation corresponds to a LRR band at 77 GHz.

Clause 10: The radar road reflector of clause 7, wherein the separationdistance is less than about ⅛ of the radar wavelength of operation.

Clause 11: The radar road reflector of clause 1, wherein resonators ofthe metasurface have a characteristic dimension of about 1/8 of a radarwavelength of operation.

Clause 12: The radar road reflector of clause 11, wherein the radarwavelength of operation corresponds to a SRR band at 24 GHz.

Clause 13: The radar road reflector of clause 11, wherein the radarwavelength of operation corresponds to a LRR band at 77 GHz.

Clause 14: The radar road reflector of clause 4, wherein the supportcomprises a visible-light reflector.

Unless otherwise stated, all measurements, values, ratings, positions,magnitudes, sizes, and other specifications that are set forth in thisspecification, including in the claims that follow, are approximate, notexact. They are intended to have a reasonable range that is consistentwith the functions to which they relate and with what is customary inthe art to which they pertain.

All articles, patents, patent applications, and other publications thathave been cited in this disclosure are incorporated herein by reference.

The phrase “means for” when used in a claim is intended to and should beinterpreted to embrace the corresponding structures and materials thathave been described and their equivalents. Similarly, the phrase “stepfor” when used in a claim is intended to and should be interpreted toembrace the corresponding acts that have been described and theirequivalents. The absence of these phrases from a claim means that theclaim is not intended to and should not be interpreted to be limited tothese corresponding structures, materials, or acts, or to theirequivalents.

The scope of protection is limited solely by the claims that now follow.That scope is intended and should be interpreted to be as broad as isconsistent with the ordinary meaning of the language that is used in theclaims when interpreted in light of this specification and theprosecution history that follows, except where specific meanings havebeen set forth, and to encompass all structural and functionalequivalents.

Relational terms such as “first” and “second” and the like may be usedsolely to distinguish one entity or action from another, withoutnecessarily requiring or implying any actual relationship or orderbetween them. The terms “comprises,” “comprising,” and any othervariation thereof when used in connection with a list of elements in thespecification or claims are intended to indicate that the list is notexclusive and that other elements may be included. Similarly, an elementproceeded by an “a” or an “an” does not, without further constraints,preclude the existence of additional elements of the identical type.

None of the claims are intended to embrace subject matter that fails tosatisfy the requirement of Sections 101, 102, or 103 of the Patent Act,nor should they be interpreted in such a way. Any unintended coverage ofsuch subject matter is hereby disclaimed. Except as just stated in thisparagraph, nothing that has been stated or illustrated is intended orshould be interpreted to cause a dedication of any component, step,feature, object, benefit, advantage, or equivalent to the public,regardless of whether it is or is not recited in the claims.

The abstract is provided to help the reader quickly ascertain the natureof the technical disclosure, It is submitted with the understanding thatit will not be used to interpret or limit the scope or meaning of theclaims. In addition, various features in the foregoing detaileddescription are grouped together in various embodiments to streamlinethe disclosure. This method of disclosure should not be interpreted asrequiring claimed embodiments to require more features than areexpressly recited in each claim. Rather, as the following claimsreflect, inventive subject matter lies in less than all features of asingle disclosed embodiment. Thus, the following claims are herebyincorporated into the detailed description, with each claim standing onits own as separately claimed subject matter.

What is claimed is:
 1. A radar road reflector comprising: a metasurfacehaving a plurality of resonators, wherein the metasurface includes asubstrate supporting the plurality of resonators, wherein themetasurface has an area, wherein the plurality of resonators supportplasmonic transfer of incident radiation across the surface, and whereinthe metasurface provides a radar cross section that is larger than aradar cross section of the area of substrate itself without theplurality of resonators.
 2. The radar road reflector of claim 1, furthercomprising a support that supports the metasurface.
 3. The radar roadreflector of claim 2, wherein the support is configured for applicationto a road surface.
 4. The radar road reflector of claim 3, wherein thesupport is made of high-impact plastic.
 5. The radar road reflector ofclaim 1, wherein the metasurface comprises a fractal plasmonic surface(FPS).
 6. The radar road reflector of claim 5, wherein the FPS comprisesa plurality of resonators having fractal shapes separated from oneanother.
 7. The radar road reflector of claim 6, wherein resonators ofthe FPS are separated by a separation distance of about 1/10 to about ½of a radar wavelength of operation.
 8. The radar road reflector of claim7, wherein the radar wavelength of operation corresponds to a SRR bandat 24 GHz.
 9. The radar road reflector of claim 7, wherein the radarwavelength of operation corresponds to a LRR band at 77 GHz.
 10. Theradar road reflector of claim 7, wherein the separation distance is lessthan about ⅛ of the radar wavelength of operation.
 11. The radar roadreflector of claim 1, wherein resonators of the metasurface have acharacteristic dimension of about ⅛ of a radar wavelength of operation.12. The radar road reflector of claim 11, wherein the radar wavelengthof operation corresponds to a SRR band at 24 GHz.
 13. The radar roadreflector of claim 11, wherein the radar wavelength of operationcorresponds to a LRR band at 77 GHz.
 14. The radar road reflector ofclaim 4, wherein the support comprises a visible-light reflector.